The normal method used by dentists to prepare a tooth for the reception of a crown involves the cutting down of the tooth to provide a generally conical spike on the tooth stump. If the crown to be mounted on the spike is a full crown, the tooth is cut at the base of the spike to provide a ledge on which the base of the crown rests when it is mounted on the spike. In practice, this ledge is cut below the gum line with some ensuing damage to the gum tissue so that when the gum recovers from the lesions it covers the parting line between the crown and tooth stump and provides a natural barrier to the entrance of bacteria, mouth secretions, and food particles to the space between the tooth stump and crown.
The cutting process is usually done by the dentist through the use of several different types of abrasive cutting tools and the ultimate success or failure of the work depends much on the skill of the dentist in forming the ledge and spike for the reception of the crown. The crowns are made from impressions of the stump and if, in the process of preparing the stump, the dentist has made undercuts in the spike area, it not infrequently happens that the prepared crown fails to properly fit on the spike and the base of the crown inadequately seats against the ledge of the tooth stump. Under such circumstances the gum frequently fails to cover the parting line as it recovers from the lesions and this, of course, provides an exposed area where food particles, bacteria, and mouth secretions can seep into the space between the crown and tooth stump.
Attempts have been made to design a cutting tool that would remove much of the dental skill factor required to obtain an undercut free spike during the preparation of the tooth stump. Such attempts have usually centered around the use of a hollow cutting tool for shaping the lateral side wall of the spike. However, such attempts have left the dentist with the need to use other cutting tools in order to shape the apex area of the spike and to shape the ledge at the base of the spike when a full crown is contemplated. The need for using several different types of cutting tools is, of course, time consuming to the dentist and it also gives rise to added patient discomfort. There is, accordingly, a need in the dental profession for a single tool that can be used to not only shape the crown and lateral wall areas of the spike but also the below gum line ledge desired for mounting full crowns.
Several practical problems have been encountered in seeking a cutting tool of the type contemplated. For one, many dental patients have overcrowded teeth situations. This detracts from the use of hollow cutting tools because their sizes gives rise to damage to the enamel of adjacent teeth.
Yet another problem which has been encountered is that of dissipating heat which is generated through the use of such cutting tools. The abrading surfaces which are encountered in such spike shaping tools are vastly greater than the more conventional cutting tool attachments for dental drills. This fact, coupled with the high speed drilling equipment that is now conventionally found in the dental trade results in the generating of a large amount of heat with the resulting discomfort to the patient. Furthermore, the hollow nature of the cutting tools and the high speeds involved make it difficult to flood the work area with cooling water and air in accord with conventional procedures. Furthermore, the effective dissipation of generated heat without interfering with the dentist's view of the work area and his ability to adequately manipulate the cutting tool is of major concern.